XHTML Validation Error

The Qualaroo JavaScript code is using an HTML5 attribute called async that allows the script to load asynchronously (in the background) for visitors that are using modern web browsers. While async is a valid HTML5 attribute, it isn’t a valid XHTML attribute, causing it to give an error for current W3C XHTML validation. Despite the error, the script often will still work for your customers. If validation is important to you, then you can safely remove the async attribute to let the code pass XHTML validation.